The invention relates to a device and a method for detecting depth and color information of an object.
Such a device and such a method are extremely important in the field of quality assurance during a process for producing an object, since the depth information can be used to detect whether or not the object has a shape defect. An optical 3D measurement method is customarily used to detect the depth information.
Laser triangulation is disclosed as a 3D measurement method by a book entitled: Bildverarbeitung und optische Mexcex2technik [Image Processing and Optical Measurement Techniques] by B. Breuckmann, Franzis Verlag, 1993, ISBN 3-7723-4861-0, pp. 127-128. A laser is used to project a light point onto an object to be measured. A light beam reflected from the object to be measured is received by a photosensitive detector. The position of the object which is point marked by the light beam is calculated by triangulation from the geometry of the measurement setup and an angle between the projection direction of the laser and the direction of the light beam reflected from the object. The term xe2x80x9cprojection direction of the laserxe2x80x9d is intended to mean an axis along which the laser is aligned and along which the laser beam is projected.
The object can be measured two-dimensionally by scanning the laser beam, i.e. guiding the laser beam line-by-line over the surface of an object. In general, an elaborate opto-mechanical system is needed for scanning the laser beam.
Another disadvantage of laser triangulation is the measurement time needed for measuring an object. In the case of measuring a moving object, the measurement speed that can be achieved in the scope of laser triangulation is insufficient to measure the object fully.
Furthermore, laser triangulation is unsuitable for measuring a person, since a laser beam striking one of the person""s eyes can cause damage to the eye.
An improvement of the measurement method for detecting depth information of an object, with respect to the disadvantages mentioned above, is obtained by changing from a point projection method to an extended projection method. That approach is the basis for a topometric measurement method using structured light, as is disclosed by the book entitled: Bildverarbeitung und optische Mexcex2technik [Image Processing and Optical Measurement Techniques] by B. Breuckmann, Franzis Verlag, 1993, ISBN 3-7723-4861-0, pp. 129-138.
In a topometric measurement method using structured light, a predeterminable pattern (structure) is projected onto an object to be measured through the use of a projector and through the use of a transparent support which carries the pattern and is fitted in front of or behind the lens of the projector. The object pattern which becomes visible on the object to be measured is captured by a video camera. The position of the associated object point can be determined quantitatively for each pixel in the video-camera picture according to the laws of triangulation with the aid of the recorded picture and the pattern which is visible thereon.
In the case of a stripe projection method according to product information sheets for the Line Projector Type LCD-320, AWB GmbH, Gutenbergstraxcex2e 9, D-72636 Frickenhausen [Germany], February 1998, a periodic grid is projected onto an object. A stripe pattern which becomes visible on the object is captured by a camera, which is disposed at a predetermined angle with respect to the projection direction. In that case, the projected periodic grid is selected in such a way that the geometry of the stripes which become visible can be identified by using the camera. The position of the associated object point can be determined quantitatively for each pixel in the camera picture according to the laws of triangulation with the aid of the recorded stripe picture.
The methodology for positional determination of an object in the scope of the stripe projection method will be summarized below with the aid of FIG. 2. The stripe projection method also has disadvantages.
Since the stripe projection method requires the projection of a visible stripe pattern onto an object, further optical analysis which may possibly need to be carried out at the same time as the detection of the depth information of the object, for example analysis with respect to the color of the object, is no longer possible.
A color Charge-Coupled-Device camera (color CCD camera) is generally used to detect color information of an object. A digital red-green-blue color CCD camera (RGB color CCD camera) is disclosed by product information sheets entitled: EHD RGB Color CCD Camera TK-1270E, http://www.ehd.de/tk-1270.htm, September 1997.
That digital RGB color CCD camera delivers digital camera pictures with a resolution of 752xc3x97582 effective pixels. Color information is assigned to each pixel for storing or further processing a digital picture in the scope of image processing. It is determined from the RGB intensity composition of a color hue at a surveyed object point. The term xe2x80x9cRGB intensity compositionxe2x80x9d is intended to mean an intensity which corresponds to superposition of a first spectral color red, a second spectral color green and a third spectral color blue with their respective intensities resulting in a specific color hue.
Expressed more clearly, any color hue can be produced by superposition of the first spectral color red, the second spectral color green and the third spectral color blue with known respective intensities.
The camera has three acquisition channels, each having a CCD chip which is used to determine the corresponding intensity of the first spectral color red, the second spectral color green and the third spectral color blue of a color hue of a light beam which is reflected from an object point and then strikes the camera.
Furthermore, product information sheets entitled: Richter Enterprises Solution for Optics and Imaging, Optical Prism Assembly Data Sheet, November 1994, disclose a modification of a color CCD camera. That camera has an additional acquisition channel with a CCD chip which registers the intensity of an infrared beam striking a pixel of the camera.
It is possible to determine color information of a surveyed object by using the color CCD cameras presented above.
In order to carry out comprehensive quality assurance of a production process, it would be desirable to have a measurement system with which it is easy to determine depth and color information of an object.
It is accordingly an object of the invention to provide a device and a method for detecting depth and color information of an object to be surveyed, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provide a simple way of detecting depth information and color information of an object to be surveyed.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for detecting depth and color information of an object to be surveyed, comprising a projection unit which is constructed in such a way that a predetermined radiation pattern (wave pattern) having first waves with at least one first wavelength in a spectral range outside the light visible to a human, can be projected. A collector unit includes at least one first and one second subunit. The first subunit is constructed in such a way that the first waves can be processed, and the second subunit is constructed in such a way that second waves, which have at least one second wavelength in the spectral range of the light visible to a human, can be processed. An evaluation unit, which is coupled to the collector unit, is constructed in such a way that the depth and color information of the object, from which the first waves and/or the second waves are at least partially reflected, can be detected from signals received by the collector unit.
With the objects of the invention in view, there is also provided a method for detecting depth and color information of an object to be surveyed, which comprises projecting a predetermined wave pattern having first waves with at least one first wavelength in a spectral range outside visible light. Waves which have been at least partially reflected from the object and which include the first waves and second waves are received. The second waves have at least one second wavelength in the visible-light spectral range. The depth and color information of the object are detected on the basis of the waves.
A special advantage of the invention is that depth information and color information of an object can, if desired, be detected at the same time through the use of a single measurement system. This is achieved in such a way that the depth information is determined, for example through the use of a topometric method employing structured light, by using first waves having first wavelengths which are outside the visible-light spectrum and do not therefore affect the surface color of the object. The collector unit furthermore has two subunits with which the first waves, having first wavelengths that lie in the spectral range outside visible light, are processed separately from the second waves, having wavelengths which lie in the visible-light spectral range. The detection of the color information of the object is therefore not perturbed and it can, if desired, be carried out at the same time as the detection of the depth information of the object.
An advantage of the device furthermore is that, due to the speed of the method, the object to be surveyed may be a moving object or even a person, because of the safety of the waves.
In accordance with another feature of the invention, the second subunit is constructed in such a way that the second waves, which have one second wavelength in the red-light spectral range, one second wavelength in the green-light spectral range and one second wavelength in the blue-light spectral range, can be processed. It is possible to utilize a standard RGB color CCD camera for this configuration of the invention.
In accordance with a further feature of the invention, the projection unit is constructed in such a way that infrared radiation can be projected. The first wavelengths lie in the infrared-radiation spectral range. Correspondingly, the first subunit is constructed in such a way that wavelengths which lie in the infrared-radiation spectral range can be processed.
In accordance with an added feature of the invention, the wave pattern is a stripe pattern. The underlying principles of a standard stripe projection method can therefore be applied.
In accordance with an additional feature of the invention, the evaluation unit is constructed in such a way that a picture can be determined from the signals received by the collector unit, and at least one value for the depth information and at least one value for the color information are assigned to at least some of the pixels in the picture. It is therefore possible to detect depth and color information of an object at the same time and in correspondence with the pixels.
In accordance with a concomitant feature of the invention, a plurality of collector units are provided, each of which is coupled to the evaluation unit. The evaluation unit is correspondingly constructed in such a way that the corresponding picture can in each case be determined from the signals received by the collector units. It is therefore possible to ensure that, even in the case of a complex object, all of the waves reflected from the object are received.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device and a method for detecting depth and color information of an object to be surveyed, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.